The present invention relates to a radio local area network (LAN), particularly but not exclusively, a high data rate (12 to 54 Mb/s) radio LAN with a transmission range of up to 50 meters, for example HIPERLAN2 (High Performance Radio Local Area Network ).
A radio local area network of a type to which the present invention relates comprises in a domestic environment a plurality of what is termed plug and play operating devices, such as televisions (TVs), video cassette recorders (VCRs), digital set top boxes, personal computers (PCs), wireless games, high quality audio equipment and security/monitoring devices. Typically all the operating devices operate in accordance with a time division protocol and a single radio carrier. Adjacent radio LANs operate on different radio carriers. However as the radio LANs are short range, frequency re-use can be practised in a manner similar to cellular telephone systems. Control of the radio LAN is effected by a master capable operating device acting as a central controller which allocates resource, that is down-and up-link time slots in a sequence of time frames, for a data transaction between two operating devices, for example a TV and VCR, in the radio LAN. The allocation of the resource depends on the operating devices and how much capacity they require. Since the master capable operating device can itself be switch-on and -off at random times by a user, there is a need for the radio LAN to be able to select another master capable operating device as a central controller from amongst those devices which are currently energised. However each change of central controller involves re-organising the radio LAN which is undesirable.
An object of the present invention is to enable a radio LAN to be able to select a central controller from amongst the currently energised master capable operating devices.
Another object of the present invention is to reduce the number of changes of central controller.
According to one aspect of the present invention there is provided a radio local area network comprising a plurality of wireless plug and play operating devices, one of which operating devices functions as a master device for setting-up wireless links between the operating devices, at least two of said operating devices having means for building-up a history of when the respective ones of said at least two operating devices are energised, wherein when the current master device is rendered inoperative as a master device, one of said at least two of said operating devices having the more (or most) favourable history functions as a master device.
According to a second aspect of the present invention there is provided a method of operating a radio local area network comprising a plurality of wireless plug and play operating devices, the method comprising one of said plurality of operating devices functioning as a master device for setting-up wireless links between the operating devices, at least two of said operating devices building-up a history of when the respective ones of said at least two operating devices are energised, and one of said at least two of said operating devices having a more favourable history taking-over the function of the master device in response to the current master device being rendered inoperative.
According to a third aspect of the present invention there is provided a plug and play operating device comprising means for building up a history of when it is energised.
In one embodiment of the present invention, the total on-time of each master capable operating device over a preset time period is determined and is used in selecting the next central controller.
In another embodiment of the present invention the number of times a master capable operating device is switched-on over a preset time period is determined and the inverse of the number is used in selecting the next central controller.
In a further embodiment the total on-time and the number of times that the operating device is switched-on over a preset time period are used to select the next master capable operating device to be the central controller. Preference is given to the operating device which has a total on-time composed of a smaller number of on-time periods rather than an operating device whose total on-time is composed of a larger number of on-time periods which would require frequent re-organisation of the radio LAN.
In an attempt to reduce the number of re-organisations of the radio LAN, the arbitration process used may permit a re-assessment of the selection of the master operating device in the event of another operating device being energised and joining the radio LAN, however insodoing there is a bias made in favour of the central controller function remaining with the presently selected master operating device.